The present invention relates to a terminal structure of an optical fiber bundle formed by bundling a plurality of optical fibers.
It is known to introduce light into an optical fiber bundle so as to cause the light to be guided by the optical fiber bundle to a destination. In this case, light emitted from a light exit end of the optical fiber bundle has an exit angle .theta. depending on the N.A. (numerical aperture) of the optical fiber strands used in the fiber bundle. It is known that a larger N.A. leads to a larger exit angle .theta., and that the exit angle .theta. is determined by the following expression (1) when the light exits into air EQU .theta.=2.sin.sup.-1 (N.A.) (1)
The exit angle .theta. typically has the following values for various types of optical fibers:
(1) In the case of an optical fiber composed of a core of GeO.sub.2.SiO.sub.2 and a cladding of SiO.sub.2 for use in light communication or the like. N.A.=0.3 and therefore .theta.=35.degree..
(2) In the case of an optical fiber composed of a core of SiO.sub.2 and a cladding of SiO.sub.2 and fluorine for use in ultraviolet ray guiding or the like. N.A.=0.2 and therefore .theta.=23.degree..
(3) In the case of an optical fiber composed of a core of GeO.sub.2.SiO.sub.2 and a cladding of SiO.sub.2 and fluorine for use in illumination light guiding or the like. N.A.=0.35 and therefore .theta.=41.degree..
(4) In the case of a multicomponent-glass optical fiber for use in illumination light guiding or the like N.A.=0.55 and therefore .theta.=67.degree..
As described above an optical fiber of a pure-quartz core commonly used as a light guide for ultraviolet rays has the smallest exit angle .theta..
Referring to FIG. 8 of the accompanying drawings, the use of a conventional apparatus will be described hereunder.
FIG. 8 shows a state where the inside of a vessel is subjected to ultraviolet sterilization by use of a conventional optical fiber bundle. As illustrated in FIG. 8, an optical fiber bundle 1 is disposed so as to be directed to an opening of a vessel 2 so that ultraviolet rays emitted from a light exit end surface of the fiber bundle 1 enter into the vessel 2 as indicated by the reference numeral 3 in the drawing so as to illuminate the inner surface of the vessel 2 to thereby sterilize the inner surface of the vessel 2.
Sterilization by use of the foregoing conventional apparatus, however, has been subject to the following problems. A first problem is that, in the case of a bottle-like vessel having a small opening, a lower portion of the opening indicated by reference numeral 4 in FIG. 8 cannot be sterilized at all. Further in the case of a vessel having an uneven inner surface the uneven portion often cannot be sterilized because the uneven portion cannot be irradiated with ultraviolet rays.
A second problem is that even in the case where an inner surface of a vessel is irradiated with ultraviolet rays, the irradiation is performed with a predetermined angle and therefore sufficient sterilization cannot be achieved. FIG. 9 is a diagram for explaining this phenomenon. As illustrated in FIG. 9 when the inner surface of the vessel 2 is irradiated with the ultraviolet rays 3 from the optical fiber bundle 1 with an inclination angle of .theta./2 (.theta. being an exit angle). the intensity I of irradiation is sin(.theta./2) times as large as that in the case where irradiation is performed vertically. Therefore, in the case of the foregoing optical fiber composed of a core of SiO.sub.2 and a cladding of SiO.sub.2 and fluorine. ##EQU1## Accordingly, the intensity of irradiation is lowered to about 20%.
Because the above-described problems the conventional apparatus shown in FIG. 8 has not been used for sterilization.
It is therefore an object of the present invention to provide a terminal structure of an optical fiber bundle in which it is possible to easily and accurately perform sterilization of the inside of a vessel such as a bottle or the like.